Color.Atlas.of.Endodontics-ublog.tk

Chapter Seven Obturation

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FIGURE 7-1 Note the overextension of gutta-percha and lack of	FIGURE 7-3 Diagram of two cones depicting the tapered canal and
adaptation to the canal walls.	point adaptation. The taper developed in preparing the canal provides
	resistance form that prevents extrusion when the point is seated.

FIGURE 7-2 A radiograph of a failing maxillary left lateral incisor demonstrating an overextension.

FIGURE 7-4 When the apical constriction has been lost because of inaccurate length determination or resorption, a stop can be prepared by deliberately creating a ledge within the canal space.

stop cannot be prepared (Figure 7-3). Overextension, then, may be indicative of a poor fit and a poor seal in the apical area. Bacteria and their toxins could continue to leak from the root canal, preventing apical healing. Additionally, although gutta-percha itself is relatively inert,15 sealers are not. Sealers, even when confined to the root canal, are toxic and cause periapical inflammation that can last for years. 16 Overextension of sealer into the periodontal ligament and bone can preclude healing and promote chronic inflammation.

Therefore the goals of nonsurgical root canal treatment should be to clean the canal thoroughly, remove as much bacteria and debris as possible, shape the canal into a continuously tapering cone to accommodate the

obturating material, and fill the space completely. The obturating material should fill the canal, but it should not extend beyond its confines. Respecting the apical constriction and preparing a stop for the obturating material is desirable when possible, but in many cases periapical inflammation has already caused resorption of the apex." In this case, several alternative methods can be used to confine the material to the canal. Clinicians should carefully determine the length of the tooth to the apex, then step back 1 or 2 mm and deliberately create a circumferential ledge by reaming the canal several sizes larger. This technique can be used advantageously in some canals, but can also fracture the thin apical end of the root (Figure 7-4).

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FIGURE 7-5 A radiograph of a maxillary right lateral incisor demonstrating an accessory cone extending into the periradicular tissues. This results when the master cone is not adapted circumferentially in the apical third of the root.

In reality, if the canal and the gutta-percha points are tapered, the point should enter the canal until it makes circumferential contact with the canal walls. The reason points are overextended or accessory points slide past a master cone that has stopped at the prepared length is that the master cone is making only partial contact with the canal walls (Figure 7-S). This problem can be circumvented by using solvent to customize the apical end of the point or by using a form of thermoplasticized gutta-percha.

Another method to prevent the overextension of gutta-percha is to use an apical plug. The plug can be formed of dentin removed from the canal walls; dentin packed into the apical portion of the canal can prevent extrusion. 18.19 The difficulty with dentin chips is that the clinician can never be certain exactly what is being packed into the apical portion of the canal-it seems to be a mixture of dentin, canal contents, and potentially bacteria and their by-products. This unknown mixture, if bacterially contaminated (teeth with infected, necrotic pulps frequently exhibit apical resorption), can lead to non-healing and chronic periapical inflammation .20-22 A better choice may be to mix a nearly solid mass of calcium hydroxide and create a plug of that biocompatible material in the apex of the tooth. 23 Recently mineral trioxide aggregate (NITA) has become available and is a viable option .24

OBTURATING MATERIALS

Sealers

Regardless of the obturation technique employed, sealers are an essential component of the process. Sealers fill the space between the canal wall and core obturation mate-

rial and may fill lateral and accessory canals, isthmuses, and irregularities in the root canal system. The ideal properties of an endodontic sealer were outlined by Grossman25 and are provided in Box 7-1.

The most popular sealers are grouped by type: zinc oxide-eugenol formulations, calcium hydroxide sealers, glass ionomers, and resins. Regardless of the sealer selected, all are toxic until they set. For this reason, extrusion of sealers into the periradicular tissues should be

avoided.13

Zinc oxide-eugenol and resin sealers have a history of successful use over an extended period. Zinc oxide-eugenol sealers have the advantage of being resorbed if extruded into the periradicular tissues .26 Calcium hydroxide sealers were recently introduced for their potential therapeutic benefits. In theory these sealers exhibit an antimicrobial effect and have osteogenic potential. Unfortunately these actions have not been demonstrated, and the solubility required for release of calcium hydroxide and sustained activity is a distinct disadvantage. Glass ionomers have been advocated for use in sealing the radicular space because of their dentin bonding properties. A disadvantage is their difficult removal if retreatment is required.

Sealers containing paraformaldehyde are contraindicated in endodontic treatment. Although the lead and mercury components have been removed from the formulations over time, the paraformaldehyde content has remained constant and toxic. These sealers are not approved by the U. S. Food and Drug Administration.27

Controversy surrounds removal of the smear layer before obturation. The smear layer is created on the

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canal walls by manipulation of the files during cleaning and shaping procedures. It is composed of inorganic and organic components that may contain bacteria and their by-products. In theory remnants left on the canal wall may serve as irritants or substrates for bacterial growth or interfere with the development of a seal during obturation. Although fluid movement may occur in obturated canals, bacterial movement does not appear to take place. 28 Recent evidence suggests that removal of the

smear layer can enhance penetration of the sealer into the dentinal tubules. 29,30

Removal of the smear layer can be accomplished after cleaning and shaping by irrigation with 17% ethylenediaminetetraacetic acid (EDTA) for 1 minute. Irriga

tion should be followed with a final rinse of sodium hypochlorite.

The radiopacity of sealers can be increased by adding opacifiers such as barium sulfate or silver particles. Although these opacifiers can produce an esthetically pleasing result, claims of superiority of obturation based on radiographic appearance are inaccurate. The increased radiopacity may mask voids or imperfections in the compaction and is unrelated to the quality of seal obtained. In addition, sealers with silver particles may stain the tooth structure if they are left in the pulp chamber.

Acceptable methods of placing the sealer in the canal include the following31:

•Placing the sealer on the master cone and pumping the cone up and down in the canal

•Placing the sealer on a file and spinning it counterclockwise

•Placing the sealer with a lentulo spiral

•Using a syringe

•Activating an ultrasonic instrument

The clinician should use care when placing sealer in a canal with an open apex to avoid extrusion.

Core Obturation Materials

The ideal properties of an obturation material as outlined by Grossman25 are listed in Box 7-2.

Historically, a variety of materials have been employed to obturate the root canal, falling into three broad categories: solids, semisolids, and pastes. In the early days of endodontics, because of the limitations of their equipment dentists found preparing canals to the size and shape necessary for the introduction of guttapercha points very difficult. In the 1940s, Jasper 32 introduced cones made of silver, which he claimed produced the same success rate as gutta-percha but were easier to use. Silver cones met many of the criteria for filling materials but suffered from several deficiencies. The rigidity that made them easy to introduce into the canal also made them impossible to adapt to the inevitably irregular canal preparation, encouraging leakage. When leak-

age occurred and the points contacted tissue fluids, they corroded, further increasing leakage 33 ( Figure 7-6). The

FIGURE 7-6 A mandibular left second molar treated with silver cones. Failure has occurred despite placement to the correct length.

BOX 7-2

Ideal Properties o f an Obturation Material

1.It should be easily manipulated and provide ample working time.

2.It should be dimensionally stable and not shrink or change form after it is inserted.

3.It should seal the canal laterally and apically, conforming to its complex internal anatomy.

4.It should not irritate the periapical tissues.

5.It should be impervious to moisture and nonporous.

6.It should be unaffected by tissue fluids and not corrode or oxidize.

7.It should not support bacterial growth.

8.It should be radiopaque and easily discernible on radiographs.

9.It should not discolor tooth structure.

10.It should be sterile.

11.It should be easily removed from the canal if necessary.

corrosion products themselves were cytotoxic, 34 which impeded periapical healing.

At the opposite end of the rigidity spectrum are the pastes. Pastes also fulfill many of the criteria listed previously and can easily adapt to the most complex internal anatomy. However, their extreme flowability can be a negative factor, and overextension or underextension is a frequent result of using a paste technique.35 The movement of the material occurs along the path of least resistance; pressure is required for the material to flow laterally to fill the anatomic variations of the canal. If less pressure is required to flow through the apex than to flow laterally, the material will flow through the apex. Unfortunately, the operator has no way of knowing where the material is

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FIGURE 7-7 A mandibular left second molar treated with a Sargenti formulation paste. Note the unfilled mesial canals and the extrusion of material into the mandibular canal, which resulted in paresthesia.

A B

FIGURE 7-8 A, A treated mandibular left second molar exhibiting mesial bone loss. B, On flap reflection a vertical root fracture was detected.

flowing except by exposing a radiograph. By the time the radiograph develops, retrieval of overextended material becomes a surgical matter. Additionally, pastes have been associated with the addition of undesirable and toxic chemicals such as paraformaldehyde, which can produce irreversible tissue damage when extended beyond the confines of the root canal system (Figure

7).36,37

Currently gutta-percha, a semisolid material, is the most widely used and accepted obturating material.38 Chemically, gutta-percha is the trans isomer of polyisoprene, a naturally occurring relative of rubber. In the production of dental obturating cones, approximately 20% gutta-percha is combined with approximately 65% zinc oxide, 10% radiopacifiers, and 5% plasticizers. Clearly, what clinicians refer to as gutta-percha is really a compound composed primarily of other substances. Unlike rubber, gutta-percha cannot be compressed by pressure, being less compressible than water,

which is considered incompressible.39 Excessive condensation pressure cannot cause flow of gutta-percha and does not improve the seal of a root canal fill 40 but can fracture roots (Figure 7-8). Gutta-percha can be

made to flow if it is modified by either heat or solvents. Gutta-percha exists in two distinctly different crystalline phases, which Bunn termed "alpha" and "beta" modifications.41 The naturally occurring form is the alpha form, which melts when heated above 65° C. If it is cooled extremely slowly, the alpha form will recrystallize. If it is cooled routinely, the beta form recrystallizes, which is the form in which most gutta-percha exists. Although the mechanical properties of the two forms are the same, when alpha phase gutta-percha is heated and cooled, it undergoes less shrinkage than the beta form, making it more dimensionally stable for use with ther-

moplasticized techniques.

In addition to its ability to conform to canal irregularities, gutta-percha exhibits very low toxicity, being es-

Chapter Seven Obturation

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FIGURE 7-11 A .20 series GT file and a .04 gutta-percha cone.

FIGURE 7-9 Gutta-percha is relatively inert in periradicular connective tissues.

FIGURE 7-10 Nonstandardized (top) and standardized (bot-	FIGURE 7-12 A, Master cone in place with finger spreader.
tom) cones.	B, Accessory cone placed in space created by the finger spreader.
	C, Accessory cones in place, completing the obturation process.

sentially inert when in contact with the periapical tissues (Figure 7-9).42,43 Additionally, it is easily removed if post space is needed or if retreatment becomes necessary. Gutta-percha does not adhere to the canal walls even when thermoplasticized and still requires a sealer to prevent leakage. 44,45

Gutta-percha cones are available in two forms: nonstandardized and standardized (Figure 7-10). The nonstandardized cones have relatively small diameter tips compared with their larger bodies. Their nomenclature refers to these two dimensions-a "fine-medium" cone has a fine tip and a medium body. Standardized cones are designed with an overall 0.02 mm / mm taper, to match the taper of endodontic files. Recently, as files of various tapers have been introduced, different tapers of gutta-percha cones are now being manufactured (Figure 7-11).

TECHNIQUES

Clinicians should be able to use a variety of obturation techniques because each case is unique and may require

modification of routine procedures for an optimal result. The following are common obturation techniques currently within the standard of care.

Lateral Condensation

Lateral condensation is the most common technique for obturating the root canal space. This technique can be used in most clinical situations and can be modified to facilitate unusual cases. Before performing obturation with lateral condensation, the clinician prepares the root canal in a continuously tapering manner to an endpoint that ideally coincides with the minor constriction ,46 often referred to as the working length. A standardized point (the "master cone") is selected with a diameter that is consistent with the largest file used in the canal at the working length (Figure 7-12).

The clinician grasps the master cone with forceps at the point where the distance from the forceps to the tip is equal to the working length and inserts it into the canal. If the fit is correct, the point will exhibit "tugback," or resistance to removal at working length. A

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FIGURE 7-13 An ovoid distal canal of a mandibular molar with	FIGURE 7-14 Adaptation of the master cone can be accom-
a master cone in place.	plished by softening the point in a solvent such as chloroform.

radiograph is exposed to verify that the point is correctly positioned in the canal. The cone is then removed, coated with sealer, and reinserted.

Nonstandard points are used to obliterate the remaining space. A spreader is selected that matches the length of the canal and the taper of the points. Finger spreaders provide better tactile sensation and are less likely to induce fractures in the root than the more traditional D-1 1T spreader . 47 Nickel-titanium spreaders provide increased flexibility, reduce stress, and penetrate deeper compared with stainless steel instruments. 41,41 The spreader is introduced into the canal to a depth that approaches within 1 mm of the working lengths° and rotated to create a space lateral to the master cone for placement of an accessory cone. The process is repeated, with the cones being condensed until the spreader can no longer penetrate the mass. Only light pressure is required because the gutta-percha is not compressible and because as little as 1.5 kg of pressure is capable of fracturing the root.51 The excess gutta-percha in the chamber is then seared off and lightly vertically condensed with a heated plugger approximately 1 mm below the orifices to the canals or the cementoenamel junction in anterior teeth.

Apical Modification with Solvent

A disadvantage to lateral condensation of gutta-percha is that the material does not conform to the irregularities of the canal. Although lateral condensation reduces the space between the obturating cones, unfilled areas ( "voids") remain as potential paths for leakage.52 Because the preparation of a completely round canal is impossible and because the crucial apical area of the canal is likely to contain lateral canals, the tug-back experienced and the image displayed on a two-dimensional radiograph may give a misleading impression of a dense

fill. In reality only point contact may exist between the core and the walls of the canal (Figure 7-13). This situation is often discovered when an accessory point extends into the periapical area despite a seemingly well-placed master cone (see Figure 7-5).

To overcome this shortcoming, the clinician can temporarily soften the tip of the point by dipping the master cone in a solvent (chloroform, halothane, or eucalyptol) for several seconds and placing the softened point in the canal (Figure 7-14). This produces an impression of the apical portion of the canal in the material. The clinician then removes the cone from the canal for a few moments to allow the solvent to evaporate, applies the sealer, and replaces it so that it is oriented in the same direction as when the impression was made. 53 Although concerns have been raised about the use of chloroform in the dental operatory, evidence indicates that it is safe to use the material for fabricating custom cones and for retreatment.14,55

Although standardized cones are available from size 15 (0.15 mm) to 140 (1.40 mm), occasionally a canal is encountered that exceeds these dimensions. In such cases a customized gutta-percha point can be created by rolling several warmed gutta-percha points together with a cement spatula on a glass slab. The point is cooled with water and the size is tested in the canal and rerolled until an approximate fit is achieved. Solvent dip may then be used to further adapt it to the walls of the canal. Sealer and accessory points can then be used as previously described (Figure 7-15).

Warm Lateral Condensation

Warm lateral condensation is a variant of traditional lateral condensation. A heated instrument is introduced into a tooth already obturated by lateral condensation to soften the gutta-percha mass and enhance adaptation to

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FIGURE 7-16 An Endotec instrument used for warm lateral condensation.

A

C

FIGURE 7-15 A, A master cone fabricated by rolling several gutta-percha cones together on a glass slab. B, A standardized cone compared with the fabricated cone. C, Obturation of a large canal in a maxillary right central incisor using a rolled gutta-percha cone.

the internal anatomy of the canal. This technique is useful to increase the adaptation and density of teeth obturated with lateral condensation, but it is especially indicated for teeth with internal resorptive defects and C-shaped canals. Liewehr et a156 demonstrated a nearly 15 % increase in weight after the use of the Endotec (Lone Star Technologies, Westport, CT) device (Figure 7-16). The Endotec is a battery-powered spreader, the tip of which heats to approximately 350° C when activated. One technique, called the "zap-and-tap" technique ,57 was devised to avoid the problems caused when accessory

FIGURE 7-17 Obturation of a mandibular premolar with internal resorption using the zap-and-tap technique.

points placed during warm lateral condensation are heated and subsequently removed en masse when the Endotec spreader is withdrawn. In the zap-and-tap technique the canal is filled by lateral condensation and the excess gutta-percha removed. The Endotec instrument is then activated (the "zap") for 4 to 5 seconds and moved in short, continuous motions in and out of the gutta-percha mass. As the gutta-percha becomes warm, the tip of the Endotec instrument sinks further into the mass with each successive tap. When continued tapping fails to cause the tip to penetrate further or when the tip is within 2 mm of the working length, a cold spreader is introduced and rotated to condense the thermoplasticized gutta-percha into the canal anatomy. Accessory points coated with sealer are then added until the canal is completely obturated (Figure 7-17). The same technique can be used with the Touch `N Heat (Kerr Division, Sybron Digital Specialties, Inc., Orange, CA) instrument or with the System B (Analytic Endodontics, Sybron Dental Specialties, Inc., Orange, CA) instrument using Touch `N Heat tips.-5 8 Alternatively, an ultrasonically activated spreader may be used. 59

Warm lateral condensation has many advantages. Since it follows cold lateral condensation, heat is not introduced to the apex of the tooth. The technique also allows precise length control in the placement of the guttapercha and permits filling of voids, isthmuses, C-shaped canals, lateral and accessory canals, and internal resorptive areas. The potential for root fracture is reduced because the thermoplasticized gutta-percha mass flows easily into the anatomic variations with light spreader pressure. It is an easy technique to learn and requires only a relatively inexpensive addition to the armamentarium. Warm lateral condensation does not require preheating

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or special gutta-percha. In addition, cleaning and sterilization procedures are not complex.

Warm Vertical Condensation

In 1967, Schilder8 advocated vertical condensation with warm gutta-percha as an alternative technique to cold lateral condensation or silver points. He recognized the importance of three-dimensional obturation of the entire root canal system and was concerned about the potential for voids and incomplete obturation occurring with other techniques. 52 The principal advantage of warm vertical condensation is its ability to adapt the warmed and softened gutta-percha to irregularities and accessory and lateral canals within the root canal system. 6o,61

Warm vertical condensation relies on the placement of a gutta-percha point, the removal of all but the apical portion of the cone with heat, and the addition of small segments that are heat-softened with a spreader and compacted vertically with a plugger. This produces a homogeneous mass throughout the root canal. Furthermore, because the hydraulic pressure forces gutta-percha and sealer into anatomic variations, the technique is noted for its demonstration of lateral and accessory canals radiographically.

The armamentarium needed consists of spreaders and pluggers. The spreaders are not used to condense the cold gutta-percha cones together, but rather serve as heat carriers to soften the gutta-percha mass before condensation with the cold plugger. The pluggers come in a variety of sizes (8 [0.4 mm], 8 1/2 [0.5 mm], 9, 9'/, 10, 10 1/2 11, 11'/, 12) of increasing diameter and are marked at 5-mm intervals (Figure 7-18). After the root canal is ready for obturation, prefitted pluggers are selected that will enter the canal and descend to the desired depth. The clinician can mark the length by placing rubber stoppers on the cylindrical shaft of the instrument. Marking the pluggers in this manner allows the clinician to apply force to the gutta-percha mass while limiting the force applied to the canal walls.

A nonstandard gutta-percha point is selected and its tip cut away until it fits with tug-back approximately 2 or 3 mm short of the working length. The point is then coated with sealer and used to place and distribute sealer within the radicular space. A flame-heated red-hot carrier (spreader) is used to sear off the point at the orifice of the canal. Heavy vertical pressure is immediately applied with the largest cold plugger to force the cone apically. Because only the coronal 3 to 4 mm has been heated, the spreader is again heated and carried 3 to 4 mm further into the gutta-percha mass, followed by strong vertical condensation with the appropriate size plugger. This process softens and removes much of the gutta-percha, forcing it laterally and vertically into the irregularities of the canal. The procedure is repeated until the center of the canal is essentially empty except for the apical 5 mm. The clinician then refills the canal by touching the surface of the apical mass with the heat car-

FIGURE 7-18 Schilder (Dentsply Maillefer, Ballaigues, Switzerland) pluggers used for warm vertical condensation. These instruments are manufactured from size 8 to size 12 with half sizes.

rier, placing a warmed 2- to 4-mm segment of guttapercha in the canal, and condensing it vertically, repeating this process until the canal is filled (Figure 7-19).

Although the classic vertical condensation technique is capable of producing a dense, homogeneous root canal filling, there are several disadvantages. The technique is difficult to master and time consuming. It is particularly difficult to use in curved canals where the straight, rigid pluggers are unable to penetrate to the necessary depth. To allow the rigid carriers to contact the gutta-percha within 4 or 5 mm of the apex, the canals must be prepared larger and more tapered than in the lateral condensation technique, requiring the removal of additional dentin, which weakens the root. In addition, enormous pressures are created in the apical portion of the root, producing more fractures than lateral condensation . 62

Because of these limitations, modifications to the technique have been suggested. One two-step technique consists of placing the sealer-coated initial gutta-percha point, then using a small spoon-shaped curette heated red hot to remove the coronal portion 8 to 10 mm inside the canal in anterior teeth. The portion of the point

that was removed is set aside. A heat carrier is used to heat the apical portion, followed by heavy condensation with a plugger as before. The superficial part of the coronal apical gutta-percha mass is heated, and the reserved portion is warmed, reinserted into the canal, and condensed to fill the remainder of the canal. This simplified technique saves time but does not reduce the condensation pressures and may actually increase them.

A recent modification advocated by Ruddle 63 employs a similar technique for the placement and removal of the gutta-percha point, a process he terms "down packing." With this technique a thermostatically controlled heat source, the Touch `N Heat instrument (Figure 7-20), is used instead of flame-heated spreaders. The

Chapter Seven Obturation

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A

C

FIGURE 7-19 Diagram of the warm vertical condensation technique. A, After a heated spreader is used to remove the coronal segment of the master cone, a cold plugger is used to apply vertical

pressure to the softened master cone. B, Obturation of the coronal portion of the canal is accomplished by adding a gutta-percha segment. C, A heated spreader is used to soften the material.

D, A cold plugger is then used to apply pressure to the softened gutta-percha.

FIGURE 7-20 The Touch `N Heat is used in warm gutta-percha techniques. (Courtesy Sybron, Inc. Orange, CA.)

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second phase, refilling of the canal, is accomplished using the Obtura (Obtura Corporation, Fenton, Maryland) instrument, which is an electrically heated guttapercha "gun" that heats gutta-percha to a flowable consistency and then expresses it into the canal through a 23-gauge needle. The canal is filled by injection and condensation of 4- or 5-mm segments. This step is referred to as "back-packing." The technique is somewhat faster and because it uses uniformly softened guttapercha from the Obtura gun (Figure 7-21), it requires less pressure than the standard technique. Unfortunately, the down-packing portion produces the same pressures in the apical end as the Schilder technique, and because the same pluggers are used, identical amounts of tooth structure must be sacrificed for their introduction. Additionally, the technique is difficult to master and requires a considerable armamentarium to employ.

Continuous Wave Obturation

Buchanan recently introduced the continuous wave of condensation technique as a modification of the warm vertical compaction technique for canal obturation. This technique requires a smooth tapering funnel, an apical constriction, and appropriate master cone adaptation. The technique is often employed after cleaning and shaping procedures using nickel-titanium rotary files. GT

( Dentsply, Tulsa Dental, Tulsa, OK) gutta-percha points are now manufactured to mimic the dimensions of the GT files. The System B heat source is an electric device that supplies heat to a plugger on demand (Figure 7-22). Pluggers are available in standardized sizes, as well as nonstandardized sizes that match conventional guttapercha cones. Cones and pluggers that match files of greater taper are also available (see Figures 7-11 and 7-23). Several hand pluggers are available.

Heat is applied using the System B heat source at the prescribed temperature (200° C) for a period of time determined by the operator. Applying a constant source of heat to a prefitted gutta-percha cone softens the guttapercha so the clinician can apply hydraulic pressure in one continuous motion. As the plugger moves apically the cone adaptation is more precise and the hydraulic pressure increases, forcing the gutta-percha into canal irregularities and accessory canals.

With the continuous wave technique a master cone is adjusted to fit at the corrected working length and cut back 0.5 mm. The largest plugger that will go to a depth 5 to 7 mm from the apex is selected, and the reference point is marked with a stop. The master cone is coated with sealer and used to coat the canal walls. The System B heat source is set to 200° C and placed in touch mode. The master cone is severed at the canal orifice and re-

FIGURE 7-22 The System B unit.

FIGURE 7-21 The Obtura is used for thermoplastic injection	FIGURE 7-23 A System B plugger and a nonstandardized gutta-
techniques and back-filling procedures with other techniques.	percha point.